Manufacture of railway and tramway rails



. atented Aug. 16, 1938 UNITED STATES PATENT OFFICE MANUFACTURE or RAILWAY AND TEAM- WAY RAILS Application July 8, 1931, Serial No. 549,580

ll Claim.

My invention relates to improvements in the manufacture of railway and tramway rails and the object of the invention is broadly to provide an improved manner of treating and handling the rails during a certain stage of their manufacture whereby the strength, durability and general quality thereof will be greatly improved and whereby certain very serious and undesirable features hitherto present in such rails may be positively eliminated.

A further object is to eliminate the presence of shatter cracks in such rails and thus the formation of interior fissures which develop within such rails as a result of such cracks and also to eliminate the many dangers and disadvantages consequent thereupon.

A further object is to accomplish the above by a. novel and improved manner of treating the rails which will readily lend itself to convenient adaptation to the ordinary rail mill without seriously interfering with or delaying the regular operations of such mills.

A further object is to accomplish the desired results by subjecting the rails to a retarded rate of cooling over a temperature range below the critical range and carrying this retarded cooling rate down to a temperature much lower than has hitherto been recommended or practiced.

A further object is to obtain the desired retarded rate of cooling by providing in a novel manner, a thermal protection for the rail.

A further object is to provide this thermal protection in the form of a thermally protective enclosure separate from the mill hot bed into which enclosure the rails are placed for a desired period, being removed from the mill hot bed to be placed within said enclosure, so that the desired retarded cooling rate is obtained without in any way interfering with or obstructing the normal capacity of usefulness of the mill hot bed.

A further object is to considerably reduce the length of time during which the rails remain upon "the mill hot bed, largely reducing the required hot bed area and making available space which may be utilized for the installation of the thermally protective enclosure used in carrying out the invention.

A further object is to accomplish the elimination of shatter cracks without disadvantageously (Cl. l48--21.5)

afiecting the characteristics of the rail as regards hardness and tensile strength.

With the foregoing and other objects in view, as will appear more fully hereinafter, the present invention consists in the improvements in the manufacture of railway and tramway rails, all as hereinafter more fully explained and described.

The present invention has to do with the treatment of the rail after it has cooled below the critical range and is equally applicable toall rails regardless of the manner-in which they may have been treated or handled above or within the critical range and an important feature of the present invention is that in accordance therewith the rails in cooling below the critical range are subjected to a retarded rate of cooling over a temperature range, the lower limit of which is much lower than has hitherto been practiced or even suggested.

The present invention is also applicable to rails which may have been subjected to an accelerated rate of cooling through the critical range followed by any tempering treatment somewhat below the critical range.

I am aware that hitherto rails have been subjected to a retarded rate of cooling over a portion of the temperature range below the critical range, but the lower limit of such retarded cooling has been very much above that contemplated in the present invention.

Experiments have shown that duringthe lower portion of the cooling range, say during approximately the last 300 degrees centigrade of the cooling range, peculiar changes or stresses are set up within the rail and if the rail is subjected to normal or accelerated cooling through some vital portion of this lower cooling range, shatter cracks are frequently formed whereas, if it is subjected to, retarded cooling through that vital portion, the formation of shatter cracks is entirely 49 and with certainty eliminated which is the feature of the present invention.

The type of rail failure known as interior fissure has been a steadily increasing menace to safety in railway operation for the past twenty years or more. Interior fissures may be either longitudinal or transverse. A longitudinal fissure occurring 'in a. vertical plane produces the rail failure commonly; known as split head. The fissure starts in the interior of the rail head and develops under traffic. The longitudinal rupture may work out and become a visible surface crack either on the top or underneath surface ,of the rail head, or ,may extend internally down into the web of the rail and come to the surface on the side of the rail web. Crushed head" so called is merely a form of split head" in which the-internal longitudinal rupture has caused the side of the head to bend down under traiiic before the fissure has reached the outside surface of the'rail.

When an internal longitudinal fissure occurs in a horizontal plane it develops the type of failure known variously as horizontal fissure, "longitudinal fissure", or horizontal split head.

By far the most dangerous type of internal fissure is that occurring in a transverse vertical plane in the-interior of the rail head. These fissures grow under traffic until at times the greater .part of the cross sectional area of the head may be ruptured without any surface indication to give warning of the danger. This most dangerous type of internal fissure is commonly called the transverse fissure". 5

In 1918 Mr. F. M. Waring, engineer of tests of the Pennsylvania R. R. first called attention to the presence of what appeared to be cracks in the interior of the rail head in rails which had failed through transverse fissures in the track. These apparent cracks were disclosed by planing 03 the top of the rail head to give a horizontal longitudinal face approximately in the centre of the mass of the rail head and by etching this surface in a mixture of strong hot acids. At the same time Waring detected a similar appearance of what seemed to be cracks in a new rail which had never been in the track.

In U. S. Bureau of Standards Technologic Paper, No. 156, March 1920, Messrs. H. S. Rawdon and Samuel Epstein first demonstrated that the apparent cracks disclosed by strong etching of transverse fissured rails were really cracks existent in the metal before treatment with acid. The investigation of these cracks was pursued rather slowly at first but with steadily increasing interest especially in the past few years. Railway technical men gradually accumulated evidence as to the existence of these so called "shatter cracks" in new rails and it is sufilcient to state that for several years now it. has been well known to numerous steel plant technical men that a considerable percentage of new rails show shatter. It is very difiicult to prove and to date it has not been proven that shatter cracks are essential to the development of transverse fissure failures in the track. Strong probability exists, however,

from the suspicious appearance of many of the transverse shatter cracks found in new rails, and from the very large proportion of transverse fissure failedrails, which show shatter on subsequent examination. The reported occasional failure to find shatter cracks in a flssured rail may be due to inexperience of the person making the examination, failure to examine the proper zone in the rail head, or to the existence in the original'rail of only a few shatter cracks. The crack which develops into a fissure can naturally not be disclosed in any subsequent investigation of the rail. I have frequentlydound 12" lengths tion of the rails while cooling on the mill hot beds. Covers have been placed over the hot rails and drafts from below prevented by filling in the spaces between the skid rails of the hot bed. These attempts have been unsuccessful in eliminating shatter, because the protection was inadequate and was supplied during too high a temperature range.

I have proven by a long series of tests carried out at a rail mill. during rolling, during which about twelve hundred samples of rails, systematically selected, were examined for shatter, that shatter cracks form at a decidedly lower temperature than has formerly been believed. For example samples were cut at the hot saw from a thirteen foot length of an -lb. section intermediate manganese rail (.64% C-1.43% Mn), thirteen pieces in all, each 12" long. Six pieces, evenly distributed over the 13 ft. length were allowedto cool normally in the air and all showed numerous longitudinal shatter cracks with an occasional transverse or diagonal crack. The other pieces were buried in lime for cooling after having been cooled normally in the air for various lengths of time before placing in the lime. One piece was placed in the lime immediately after cutting at the hot saw, others were cooled in the air from five minutes up to fifty-five minutes before placing in the lime. The piece cooled for fifty-five minutes in the air was held until a small puddle of half and half solder (melting point approximately 175 C.) placed on top of the head, had just frozen. All pieces allowed to,

cool in the powdered lime, even the one held fifty-five minutes in the air, were entirely free from shatter. The temperature in the centre of the rail head when the solder froze would be approximately 200 C. or slightly lower as established by subsequent test. It is not suggested that protected and retarded cooling of rails only below 200 C. is a panacea for shatter cracks. Variations in the temperature range of shatter formation will occur depending on the size of the section, the chemical composition, and the nature of the steel itself, in such particulars as size of grain, etc. My investigation has covered rail sections from 80 lbs. per yard to lbs. perv yard. The chemical. specification for the 130 lb. rail called for a carbon range of .68% to .83% and a manganese range from .'70% to 1.00%.

I have found that for all rails it is true that shatter cracks form at a decidedly lower temperature than heretofore believed.

For example I have out similar 6 it. lengths of 130 lb. rail at the hot saw and allowed these to cool in the air until visible redness in a dim light had Just disappeared. The pieces were then placed in a pre-warmed brick lined iron box provided with an insulated cover. A pyrometer was installed between the close lying rails and the air temperature observed during cooling. After three hours eleven minutes the air temperature had dropped to 149 C. at this point one piece of rail was removed and allowed to finish its cooling normally in the air of the mill, the cover of the box being immediately closed. After 6 hrs. and 10 minutes the air temperature in the box had fallen to 93 C. Another piece was removed at this temperature and allowed to finish its cooling normally in the air of the mill, the cover of the box being immediately'closed. The remaining piece of rail was left in the box for a total period of 24 hrs. after which time the air temperature in the box had fallen to approximately 24 C. A

comparison 6 ft. length from the same rail had 76 been cut at the hot saw and allowed to cool normally in the air of the mill. The actual findings on 12" long samples cut from the four pieces of rail and examined for shatter cracks was as follows:,-

C 001mg method Shatter cracllslczgnd in 12" Cooled normally in air Cooled normally in air to loss of visible redness then in insulated box to 149 C., then normally in air.

Cooled normally in air to loss of visible redness then in insulated box to 93 C. then normally in air.

Cooled normally in air to loss of visible redness then in insulated box to 24 0.

Very many longitudinal cracks and a few transverse.

Many longitudinal cracks and a few transverse.

Numerous longitudinal cracks and a few transverse.

Entirely free from cracks.

Ihe ladle analysis on the above heat was C 30%, Mn .9l%, P .032%, S .033%, Si 200% and the rail samples were all from the C rail of the same ingot.

it may here be explained that it is common practice in rail mills to mark the rails from each ingot alphabetically counted from the top to the bottom of the ingot. Thus the C would be the third rail from the top of the ingot and as six rails were produced from each ingot during these tests, this C would be from approximately the centre of the ingot.

It should be noted that as a general rule by far more longitudinal shatter cracks are found than transverse. This seems especially true in the type of rails known as intermediate manganese.

Furthermore I have found that the heavier the rail section, and the higher the content of carbon, manganese and silicon, the greater is the apparent tendency to develop shatter cracks. Many heats show no trace of shatter but I have not been able to connect the shatter results with variations in the steel making practice, and am inclined to attribute the variations in shatter to conditions in the rail rolling mill itself.

Whatever the cause of shatter I have found that ."i can entirely remove all traces of it from rails on the large scale. This has been proven over a, period where whole heats of rails as well as part heats have been treated by my process in sections from 85 lbs. to 130 lbs. per yard. No doubt exists that the process would be equally effective on all sections.

Although I have proven that shatter cracks the critical range has been passed, protecting the rails from rapid cooling down to a decidedly lower temperature than has heretofore been practiced or recommended. The exact temperature at which it is safe to remove the rails from the pro- 7 tected and retarded cooling will depend on the atmospheric temperature to which the rails are to be exposed. My experience indicates that the rails may be removed from their protection when their temperature has reached a point about 50 C. above the temperature of the air towhich theyare to be exposed for the final stage of the cooling. it do not limit myself to any exact figure in this regard but it have found repeatedly that shatter cracks are not always completely removed if the rails are taken from their protected cooling while at a temperature 75 C. above the air to which they are to be exposed. It is perferable to protect the cooling to a point as close as practicable to the surrounding air, the closer the better. The necessity of retarding the cooling of rails down to such comparatively low temperatures will generally make it impracticable to carry out the process on the mill hot beds.

The exact degree of protection required, or the exact maximum rate of cooling consistent with complete elimination of shatter cracks cannot naturally be specified nor do I limit myself closely in this respect. An exact description follows of the method I have used on the larger scale and which has proven 100% eifective in eliminating all traces of shatter cracks, producing as well, rails which show decidedly better qualities in the drop test with the base of the rail uppermost or, in other words, with the head in tension.

I have allowed the rails'to cool normally on the hot bed until visible redness in a dim light has disappeared, and then, as promptly as practicable, lifted the rails with a magnet equipped crane, and placed them in what I have called a cooling tank. The tank so called is a structure measuring 41 ft. in length inside, by approximately 6 ft. in width and 5 it. 6" in depth. The end walls were of brick, about 9" thick, and the long side walls consisted of one thickness of corrugated sheet iron. The iiloor of the tank was formed by the ground. The sheet iron sides ran down to the ground and were slightly banked at the bottom with earth to prevent cold air drafts. The main portion of the tank was covered (for about 30 it.) with a. cover built up from A" steel plate. The remainder of the length was covered with three separate small cover trays formed from 1 's" thick sheet iron; Samples taken of rails from the end of the tank with these lighter covers showed that they were entirely adequate. Billets (2%" sq. section), bent in U form, constituted the bottom supports and the side ribs of the tank. Longitudinal members of light angle iron tied the ribs together and formed the supports for the sheet iron sides.

The bottom tier of rails rested on the 2 billet frame members. in the case of the 130 lbs. section rails I placed 9 rails in a tier. Skid bars of 1%" sq, section separated the various tiers of which there were usually seven. A normal charge was about sixty 130 lb. rails of 39 it. length, although the number varied irom 45 to 64. rails in individual tank charges.

On all charges of the tank a portable thermocouple pyrometer was used to note temperatures, the hot junction of the thermocouple being located approximately in the centre of the cross section of the rail pile and about 7 or 8 ft. in from the end wall. (in some charges a recording pyrometer gave a continuous record of the temperature at the same point. Owing to pyrometer lag and the time necessary for the rail pile to acquire a uniform temperature by the passage of heat from the hotter head metal to the cooler webs and flanges, it was usually some little time after charging before the pyrometer showed its maximum peak temperature, say onehalf hour, depending on whether the thermocouple happened to lie closer to the head or the base of the rails, or to be nearer or farther from the surface or the nearest rail. Although I aimed to 379 C. The rails themselves were no doubtsomewhat hotter than this going into the tank, especially the head metal.

In all cases I had comparison rails cooled normally on the mill hot bed or 5 ft. pieces cut at the hot saw and normally cooled in the air of the mill. The normally cooled, rails, during the course of investigation at times showed no signs of shatter, but I had a plentiful supply of normally cooled rails with excellent examples of shatter in varying degrees of severity. In the case of the tank charge showing the lowest peak temperature, (307 C.) the comparison normally cooled rails showed decided shatter, both 1ongitudinal and transverse, yet the tank cooled rails were entirely free from the trouble.

With the above described degree of protection the rate of cooling was reasonably uniform, depending slightly on the initial peak temperature and the atmospheric conditions prevailing at the time. Typical cooling rates as shown by the pyrometer are as follows for different tank charges.

Temp. at stated intervals after N r I 't' 1 peukoc' o. 0 n1 is g rails in peak charges 1 2 3 4 5 10 i5 20 hr. hr. hr. hr. hr. hr. hr. hr.

Normally the charges were left in the tank for from 20 to 24 hours.

The rate of cooling can be somewhat faster than shown above and yet completely eliminate shatter. A pressure blower was installed at the tank and air conduits installed to suck air from one end of the tank and discharge it into the opposite end, so that the same hot air circulated lengthwise through the rail pile and was returned in an outside air conduit to the suction of the blower to be recirculated through the tank. On some charges a cold air inlet opening was provided on the suction side of the blower to draw in a controllable amount of outside air into the circulation. This cut several hours off the total cooling time and yet all such charges showed a complete elimination of shatter. The base up drop tests on charges where fan circulation-was used did not, however, show quite as good results as without fan circulation.

I do not limit myself to any definite rate of cooling. By protecting the rails more or less, by stacking them in larger or smaller piles, or by the use of fans or other artificial means the rate of cooling may be varied or may be accelerated to the maximum consistent with elimination of shatter. What I claim is the necessity of protection and retarded cooling to decidedly lower temperatures than heretofore recommended or practiced.

Base up drop tests were made on the standard A. R. E. A. drop testing machine. Interesting results were obtained. Take for example, the

130 lb. section, using a 22-ft. dro'p, and eliminating all drop test results of A rails which are affected erratically by the presence or absence of chemical segregation.

Number of full height blows required to break rail on normally cooled rails which showed no shatter cracks averaged 2.4. The number of blows required to break tank cooled rails from the same heats averaged 3.8. There were no breaks on the first blow of any piece for either type of cooling.

Number of full height blows required to break rail on normally cooled rails that showed slight shatter was 1.9 and 22% of the pieces broke on the first blow. Tankcooled rails from the same heats required an average of 2.8 blows and 8% of the pieces broke on the first blow (see below).

Number of full height blows required to break rail on normally cooled rails that showed decided shatter was 1.07 and of the pieces broke on the first blow. Tank cooled rails from the same heats required an average of 2.6 blows and only 6% of the pieces broke on the first blow.

It should be noted that 75% of all first blow breaks on tank cooled rails occurred on. a relatively small number of charges on which fan circulation, as before described, was used. I do not recommend shortening the tank cooling time by the use of a fan.

All drop tests were made after the rails had cooled over night in the open and both ordinary and tank cooled rails were thoroughly cold at the time of the tests. In no case did all the tanl: cooled tests from any one heat break on the first blow, but it was almost the general. rule on normally cooled rails, where decided shatter was found, that all the test pieces broke on the first blow.

With the retarded cooling practice as above described, both Brinell hardness tests as well as the deflection in the drop test indicate the same hardness in the tank cooled rails as in rails cooled normally on the mill hot beds.

From the foregoing, the evidence appears to be conclusive that shatter cracks form at a much lower point of the cooling range than has hitherto been realized and the present invention by providing properly controlled retarded cooling through this vital portion of the cooling range has successfully eliminated the formation of shatter cracks.

Various modifications may be made in the invention without departing from the spirit thereof or the scope of the claim and therefore the exact details set forth above are to be taken as o illustrative only and not in a limiting sense and only such limitations shall be placed thereon as are imposed by the prior art or set forth in the appended claim.

I claim:-

A process for cooling rails, comprising the steps of cooling the rails on the hot bed in the normal way from a temperature above the critical range to a temperature substantially below the critical range but not lower than 600 F., removing the rails from the hot bed, charging the rails in a multiplicity of superimposed tiers in a heat retaining enclosure, and allowing the rails to cool slowly in the enclosure.

IRWIN CAMERON MACKIE'. 

